The present invention relates to a process for the preparation of optionally substituted pyridinecarboxylic acid chlorides (picolinoyl, nicotinoyl, and isonicotinoyl chlorides) by hydrolysis of optionally substituted (trichloromethyl)pyridine compounds. The acid chlorides prepared can serve as intermediates in the preparation of optionally substituted pyridinecarboxylic acids, esters, and amides.
Pyridinecarboxylic acids and many substituted pyridinecarboxylic acids are known and are known to be preparable by the hydrolysis of the corresponding (trichloromethyl)pyridine compound in a strong acid, such as sulfuric acid or nitric acid (U.S. Pat. No. 3,317,549). It is also known that related strong acid hydrolyses can be stopped at the acid chloride stage. Carboxylic acid chlorides are typically prepared from the corresponding acids by treatment with an inorganic acid chloride, such as thionyl chloride or phosphoryl chloride. Each of these processes produces large amounts of waste products. Processes for converting (trichloromethyl)pyridine compounds to pyridinecarboxylic acid chloride compounds that are simpler and do not create such by-products would be of considerable value in the preparation of pyridinecarboxylic acid chlorides and many commercially significant pyridinecarboxylic acid, ester, and amide compounds.
It is known that chloro(trichloromethyl)pyridine compounds react with aluminum oxide at temperatures over 500.degree. C. to produce aluminum chloride, nitrogen, carbon dioxide, and carbon monoxide (U.S. Pat. No. 4,587,116).